(CBS/AP) BOSTON - Police are treating the death of Stephen Rakes, an alleged extortion victim of "Whitey" Bulger who had wanted to testify against the reputed mobster in his racketeering trial, as suspicious and say his vehicle is missing.

Rakes, 59, of Quincy, was found dead Wednesday afternoon on a street in Lincoln, Mass. He had been attending Bulger's trial in Boston almost every day and had planned to testify until the prosecution dropped him from the witness list on Tuesday.

While the cause of death remains unknown, Middlesex District Attorney Marian Ryan has said "there were no obvious signs of trauma." An autopsy is being conducted.

Rakes had owned a liquor store in south Boston in the 1980s. He claimed Bulger and his partner Steven Flemmi forced him to sell them his store at gunpoint. He described the alleged incident in an interview with CBS Boston last year.

Flemmi put the gun on the table, and then they picked up one of my children and said, you know, 'It would be a sin - would be a sin to see this child grow up without a father,'" Rakes recounted. "It was a bad day. I melted -- I didn't know what to do."

According to the station, Rakes had been furious in recent weeks ever since Kevin Weeks, a former friend of Bulger, denied earlier this month on the stand that Bulger forced Rakes to sell the store.

"Kevin continues to lie, as usual, because that's what he has to do," Rakes said the day of Weeks' testimony. "My liquor store was never for sale - never, never, never."

Bulger, the former leader of South Boston's Winter Hill Gang, spent 16 years on the run, becoming one of the FBI's Ten Most Wanted before authorities captured him and his girlfriend in California in 2011. He is charged with participating in 19 murders but maintains his innocence.